The present invention relates to an ink-jet recording head for jetting an ink droplet from a nozzle aperture by expanding and contracting the volume of a pressure generating chamber by a piezoelectric vibrator for flexural oscillation so as to print on recording medium. More specifically, the present invention relates to structure for connecting a piezoelectric vibrator and a cable.
In an ink-jet recording head for jetting an ink droplet from a nozzle aperture by expanding and contracting the volume of a pressure generating chamber by a piezoelectric vibrator for flexural oscillation, a piezoelectric vibration plate is arranged on the surface of an elastic plate which is elastically deformable corresponding to each pressure generating chamber and a driving signal is applied to the piezoelectric vibration plate via a flexible cable.
In such a flexible cable, signal lines of the same number as at least the number of piezoelectric vibrators and a common grounding conductor are normally formed on a insulating film in accordance with the array pitch of each piezoelectric vibration plate, each signal line is connected to one electrode of the piezoelectric vibrator and the grounding conductor is connected to the other electrode.
Therefore, if the recording head is miniaturized or the array density of nozzle apertures is enhanced, the width of a signal pattern formed in the flexible cable for supplying a driving signal to each piezoelectric vibrator is necessarily narrowed and its electrical resistance is increased.
As a result, the electric potential difference from the grounding conductor of each piezoelectric vibrator varies, the quantity in which the piezoelectric vibrator is displaced varies and there is a problem that as a result, the characteristic of jetting an ink droplet varies depending upon a nozzle aperture.
To reduce the increase of electrical resistance in a signal pattern, tape carrier package (TCP) technology for mounting a semiconductor integrated circuit for generating a driving signal in an area as close to a piezoelectric vibrator as possible of a flexible cable is adopted. Hereby, as the distance in which a driving signal is transmitted can be reduced, the variation among nozzle apertures of the characteristic of jetting an ink droplet can be reduced.
However, as to realize color printing and high density printing by arranging plural rows of pressure generating chambers in one head, distance between nozzle apertures in each row is required to be reduced as much as possible and the precision of fixing ink on a dot is required to be secured, a terminal for connecting to the grounding conductor, a so-called common terminal can be provided to only one end of a terminal for supplying a driving signal to the piezoelectric vibrator, a so-called segment terminal row.
Therefore, there occurs a new problem that large distance is made between the common terminal electrode located at the other end for piezoelectric vibrators and the grounding conductor, the characteristic of displacement varies among piezoelectric vibrators in the same row and among piezoelectric vibrators in different rows and the characteristic of jetting an ink droplet varies.
Particularly, in a recording head using a piezoelectric vibrator utilizing flexural displacement, the electrode which is formed on the surface of an elastic plate, as a lower electrode is required to be formed as thinly as possible to maintain the elasticity of the elastic plate, electrical resistance is increased and the above problem is more realized.
To solve such problem, a method of increasing the area of the TCP and providing a grounding conductor outside is also conceivable, however, there is a problem that the size of the whole recording head is increased.
For a recording head using TCP in which a driving signal generating semiconductor integrated circuit is mounted on a flexible cable, there is a problem that as the rigidity of the flexible cable is increased, the characteristic related to oscillation of a piezoelectric vibrator varies due to deformation when TCP is connected to a recording head chip and contact between TCP and a piezoelectric vibrator and the characteristic of jetting ink is influenced.